Traditionally, digitally controlled color ink jet printing is accomplished by one of two technologies; “continuous stream” or “drop on demand.” In both, liquid, such as ink, is fed through channels formed in a print head. Each channel includes a nozzle from which droplets are selectively extruded and deposited upon a recording surface. Continuous stream printing uses a pressurized liquid source that produces a stream of droplets that are selectively steered toward a recording surface to imagewise deposit thereon, or are captured to be recycled
On the other hand, drop on demand printing, provides droplets for impact upon a recording surface. Selective activation of an actuator causes the formation and ejection of a flying droplet that strikes the recording surface. The formation of printed images is achieved by controlling the individual formation of droplets. For example, in a bubble jet printer, liquid in a channel of a print head is heated, creating a bubble that increases internal pressure to eject a droplet from a nozzle opening of the print head. Piezoelectric actuators, such as that disclosed in U.S. Pat. No. 5,224,843, issued to VanLintel, on Jul. 6, 1993, have a piezoelectric crystal actuator in a fluid channel that flexes when an electric current flows through it, forcing a droplet out of a nozzle.
Drop on demand inkjet printing systems have traditionally suffered from a problem of limited droplet ejection frequency. Once a single droplet is ejected form the print head, the ink cavity behind the nozzle opening needs to refill with ink before a second droplet can be ejected. Additionally, the system must dampen the perturbation associated with drop ejection and the system returned to steady state conditions before the next drop can be fired. All of this places constraints onto the fire frequency of drop on demand printing systems and reduces the response time of the system.
By increasing the speed capabilities of drop on demand printing system, it becomes possible to exploit the low manufacturing costs of these systems compared to faster and more expensive counterparts. It is an object of the present invention to increase the speed capabilities of a drop on demand print system by creating continuous flow through in an internal cavity of a drop on demand style print head, and to incorporate a flow stagnation point centered at each nozzle opening in the internal flow path.